Centre main.

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trebor
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Centre main.

Post by trebor » Fri Sep 04, 2015 8:30 am

I have my centre main bottom bracket fixed to centre of a bar see photo,
http://s1149.photobucket.com/user/aquab ... .html?o=66
but when you are sheeted in tight and release tension, boom flies up until kicker stops it, this is quite a violent action, probably due in part to jamming cleat.
I have, I think a couple of options,
1) weld an hoop on top of bar, so mainsheet only pulls sideways.
2) allow block to slide from side to side along bar.
any ideas ?
Robert
Minisprint 4230
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jpa_wfsc
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Re: Centre main.

Post by jpa_wfsc » Fri Sep 04, 2015 10:39 am

This being a single hander, what you need to achieve is the boom pulled down, with the end somewhere over the corner of the transom (not on the centreline of the boat). A common way to achieve this is a very powerful kicker and a hoop so the main only pulls in and not down, or, a traveller / track across the boat. Another very effective way is to set up as per a Laser and this is also likely to be the cheapest and easiest solution.

In all cases, the last block (with or without clam cleats) needs to be fixed in the centre of the boat, otherwise you will not be able to pull down without also pulling the block up the traveller to or beyond the CL of the hull.

You will I think always hate yourself for installing a hoop in a boat like the aquabat where being able to move across the hull without having to move to the stern will be vital for fast tacking / gybing.
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TimD
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Re: Centre main.

Post by TimD » Fri Sep 04, 2015 11:05 am

The short answer is use more kicker but..... that may also be the wrong answer!

What's happening at the moment is that as well as adjusting angle of attack of the main, the sheet is also adjusting leech tension. As you heave the sheet in you pull on the leech of the main, thus tightening it, but you'll also start bending the mast which will increase fullness in the main (simultaneously draft in in main will move aft).

Solution? Raise the attachment point of the mainsheet blocks (Merlin Rocket style hoop) although I don't see that solution as workable in your boat. Another alternative is a full width traveller (yacht style): dropping the traveller fully to leeward would let you sheet the main in closer but with reduced leech tension. Again, I don't see that as workable in a Minisail (bloomin' expensive to put a decent system in too!).

In your shoes I'd start at the beginning: go for a sail in light airs and sail up a beat. Take a look at your leech; is it hooked? (Leech tell-tails are a godsend). If not then just pull on more kicker to maintain leech tension. As windspeed increases you may need more kicker to maintain leech tension with a consequent need to pull on the downhaul to pull draught forward but also help open the top of the leech to keep the boat driving forward.

The problem is that all four sail controls at your disposal (mainsheet, kicker, downhaul and outhaul) work together; adjusting one will affect what you do with the others. I'd guess (based on 40yr old memories of having tried to get centre sheeting working on a Minisail) is that a centre main on a Minisail can be made to work in a blow but you need to beef up the kicker and will be compromised in a blow.

Its also worth remembering that you'll never get a Minisail to point high and foot fast. Sail 'full and bye' to windward.

One final point: cleats on the main are useful (essential!) on yachts but just too slow on dinghies. I've always preferred a decent ratchet block. (Just my POV).

Hope that helps a bit Rob although I've probably just confused you! (Tapping out a responae on my phone whilst sat on a train doesn't help either)/

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Re: Centre main.

Post by Rupert » Fri Sep 04, 2015 11:11 am

Put a better kicker on so it takes the tension, and bung a rachet on instead of the cleat. In singlehanders I adjust the kicker tension a lot depending on conditions to allow the boom to either rise a little when I release leech tension as the wind drops, or to make sure the boom goes out horizontally in gusts with no loss of tension. With the set up you have, this should be possible to achieve, but the cleat will always make it clunky.
Rupert

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trebor
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Re: Centre main.

Post by trebor » Fri Sep 04, 2015 1:59 pm

Hi John,
Boat is Sprint.
I did not want to use centre/aft system, keeping string to a minimum, a split tail main was a option I had considered, but would still give loads of main sheet lying round your feet when sheeted in, the fore section of Sprint is very busy.

Hi Rupert,
Seems to easy a answer, more kicker, the kicker is finished now and is one designed for Sprint, 16 to 1 and fed to 2 cleats on deck, rather than the one that was borrowed from Enterprise, I can see where you are coming from though, the boom would be lower so mainsheet will pull sideways, the mainsheet pulls boom down a significant amount when approaching centre of boat, I do not think it will even pull boom to centre of boat, I will try it tomorrow.
I had thought of using a ratchet instead of a cleat, it would certainly be smoother.

Hi Tim,
Full width traveller ? (do you mean like laser Centre/aft main?).
Robert
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Re: Centre main.

Post by Rupert » Fri Sep 04, 2015 2:58 pm

Rob, don't forget that on a singlehanders you don't want the main centred, but out by the corner of the transom. For that reason you'd not want a split tailed main. The way you have it now will work, especially with a rachet in the system. Because it is all a long way forward, though, sheet loads will always be quite heavy, so don't be shy on the amount of kicker you use in any breeze, or with the amount of Cunningham you put on if overpowered. The battened sail will respond to that in ways the triangle sail won't. If you don't have a good angle of pull on the kicker, you won't be able to pull enough on, or adjust it enough - you'll need to let loads off before bearing away.
Rupert

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trebor
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Re: Centre main.

Post by trebor » Fri Sep 04, 2015 5:48 pm

Hi Rupert,
Their was a significant problem with amount of adjustment on new kicker, having to split lines to both sides of deck limits amount of pull, to get sufficient movement I have had to use another kicker pulling 16 to 1 kicker, sounds more complicated than it is, the primary kicker adjusts to estimated wind strength, 16 to 1 kicker gives micro adjustment.
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Re: Centre main.

Post by JimC » Fri Sep 04, 2015 6:25 pm

If you're running out of throw a good bet is to make the split out to the sides 4:1 not 2:1 eg 3 single blocks at the foot of the mast and one double block as the start of the cascade.

The challenge, I should think, if you have a big kicker would be excess mast and boom bend unless spars are uprated.

My preferred system on the IC is to have a bridle on the back of the carriage, roughly where you have the bar, and finish with a ratchet block on the boom.

In theory, given the same power on the mainsheet you should end up with the same string in the bottom of the boat whether its 2:1 to the stern or 4:1 to the boom centre. More complicated than that since purchases vary and so does position on the boom, but its not going to be way different.

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Re: Centre main.

Post by Nessa » Fri Sep 04, 2015 6:54 pm

Replace the bar with a rope traveller, with the sheet coming from the boom, down through a double and at right angles block which runs along the rope traveller. The sheet then goes back to the boom before coming back to a ratchet in the boat. If you want to you can make the tension (height) of the traveller adjustable for wind conditions,
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Re: Centre main.

Post by TimD » Fri Sep 04, 2015 7:52 pm

Hi Rob, I was thinking in terms of a traveller car on a metal track. These were once commonplace on dinghies. I wouldn't bother on your Sprint, it'll just get in the way and you don't really need it anyway. Id call the system used on the Laser (and most Minisails/Sprints) a rope bridle.


I think Nessa has the answer for you. Jimc also makes a good point re length of sheet.

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trebor
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Re: Centre main.

Post by trebor » Fri Sep 04, 2015 8:19 pm

Here is a photo of existing 4to1 centre main.
http://s1149.photobucket.com/user/aquab ... .html?o=44
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Re: Centre main.

Post by Nessa » Fri Sep 04, 2015 8:47 pm

If you can move that further aft then I would, maybe to the narrow part of the seat? Otherwise it would seem to me the main is doing no more than duplicating the role of the kicker. I suspect it being so far forward is a large part of the problem.

The arrangement I describe above is what I have in my contender and have replicated in other small single handers. It works well and is easy to set up. I have a few of the double blocks described in my spares box, if you want one let me know.
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trebor
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Re: Centre main.

Post by trebor » Fri Sep 04, 2015 9:14 pm

Hi Nessa,
I am having trouble visuallising set up, do you have link to picture ?

The existing system can be moved, adapted etc, this seat and rigging is a prototype, I have no difficulty pulling boom with existing setup, though I know others would struggle, I had considered fitting another boom bracket further aft, to increase leverage.

My thinking regarding rigging when I set about this re-fit, was to keep fittings and rope to a minimum, the hiking strap is fitted under rudder bracket to minimise screws, further reducing fittings, centre main, etc, however, I have finished up with a substantial number of lines across foredeck, 10 at present, with 10 cleats to fasten to, plus approx' 20 small blocks, not counting mainsheet system. "The best laid plans of mice and men" :?
picture of rigging 2 weeks ago, prior to removing Entreprise Kicker.
http://s1149.photobucket.com/user/aquab ... g.html?o=0
Robert
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Re: Centre main.

Post by JimC » Sat Sep 05, 2015 9:29 am

Dear me, yes, that's an awfully long way forward for the mainsheet. I think I'd try a fixed stern bridle with the sheet tied to the centre of the bridle up to a block on the end of the boom, then forward to a ratchet block at your present takeoff point. Its a small sail and a long boom, that ought to be enough purchase really given a powerful kicker.

The problem I've had with the moth, being way to fat for it, is that any system which requires one to move backward in the boat at all when tacking is disadvantageous.

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Re: Centre main.

Post by Nessa » Sat Sep 05, 2015 11:22 am

[url][/http://contenderworld.de/images/this-ol ... 314.jpgurl]

My link hasn't worked, but you should be able to find the pic nonetheless. I fear though that unless you can shift things back a big it won't make much difference!
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